1. Field of the Invention
The invention relates to the field of eyeglass lens production. More particularly, the invention relates to a device for retaining an abrasive pad on a lap for fining and polishing of lenses.
2. Prior Art
Ophthalmic and other types of lenses are typically produced from lens blanks of glass or plastic having two major surfaces, one of which is typically finished, and the other of which is unfinished. Cutting, fining, and polishing operations are performed on the unfinished surface of the lens blank by a machine responsive to data corresponding to a particular lens prescription. The cutting operations are usually accomplished by employing a ball mill for plastic lenses, or a grinder for glass lenses. These cutting operations generally create a lens surface closely approximating the shape of the finished lens. However, the cut surface of the lens blank is often rough and requires that subsequent fining and polishing operations be performed on the lens blank to achieve the requisite optical clarity.
The fining and polishing operations are ordinarily performed by engaging the cut surface of the lens blank with an abrasive surface having a shape that closely approximates the desired finished shape of the lens as defined by the lens prescription. This abrasive surface is referred to by those skilled in the pertinent art as a tool or xe2x80x9clapxe2x80x9d. During operation, the device to which the lens blank is mounted, moves the blank over the abrasive surface of the lap along a conforming contoured semi-spherical path, thereby fining and/or polishing the lens surface. Laps generally consist of two main components, a mounting surface or mandrel, and a removable abrasive pad that mounts on the mandrel and against which the lens blank is moved during fining and polishing operations. The shape of the mandrel must conform as closely as possible to the prescribed shape of the lens, therefore, different lens prescriptions require different laps to be used.
During fining and polishing operations, it is often necessary to lift the lens blank off of the lap and rinse the abrasive pad to remove lens material in the form of particulate that has built-up during the fining and/or polishing operations. To conventionally prevent the abrasive pad from separating from the mandrel during rinsing, a releasable adhesive is used to bond the pad to the mandrel. A difficulty associated with adhesively attaching the abrasive pad to the mandrel is that after extended periods of use it is often necessary to change abrasive. The adhesive can make separating the abrasive pad from the mandrel difficult and time consuming. In high production situations where abrasive pads are regularly replaced, significant amounts of time can be lost separating the abrasive pad from the mandrel, thereby adding to the time and expense associated with preparing lenses. For these reasons, the art is in need of an alternate pad retaining system which avoids lost time in connection with changing pads while concurrently also rendering the changing operation significantly less difficult.
The above-identified drawbacks of the prior art are overcome or alleviated by the pad retaining system of the invention.
The invention introduces unconventional pad geometry and an unconventional lap support. The features of these two elements function together to provide quick, easy and reliable pad retention on the lap while eliminating the difficulty of removal of the pad experienced by the prior art. The invention further renders such removal and replacement a very time efficient operation.
The pad of the invention is oversized relative to conventional designs to provide surface area upon which to clamp without reducing the working abrasive surface of the pad. Pads generally are defined within a circle having a diameter of about three inches. The pads of the invention are defined by a circle having a diameter of about four and one-half inches. This provides a three quarter inch annular section of pad upon which to clamp the same. Adhesive is not required.
Complementary to the pad described, a lap support including an actuator and a retainer are provided. The retainer is moveable between two positions: the first in which it is in close proximity to the surface of the lap and the second in which it has been distanced from the surface of the lap. In the first position, a pad is compressively retained between the retainer and the lap with compression being placed upon the annular area of the pad described. In the second position the compressive force of the first position is absent and a pad may be either removed from the lap or placed thereon.
The retainer is actuated to move to the first and second positions by solenoid which is/are connected thereto through connecting rods. The retainer can be operated manually or automatically in response to conditions of the system.
A significant benefit of the retainer system is that it allows automation of pad placement and replacement. Since adhesive is not required to retain the pad on the lap, a vacuum cup on a pick and place machine is employed to place and replace pads on the lap for retention without human intervention.